426 big bore kit?

6 replies to this topic
  • GetSumBaby

Posted May 07, 2007 - 02:48 PM


I road my friends 450 the other day and was very surprised how much more power it had over mine. I figured it would be better to get a big bore kit and some head work rather than losing my butt on my bike and forking out more for a new one. And I like my green sticker and 5 speed.

Anybody have any information on this? And how bigthe kit is, where to get it?

Does the bike over-heat? Problems with jetting? and so on....


I found this .. http://www.designhap...ice-Yamaha.html


Posted May 07, 2007 - 05:42 PM


Here's a 444cc kit from MaxPower. Rick Peterson designed, so you know it's good.


  • 642MX

Posted May 07, 2007 - 07:45 PM


Big bore kits are reliable, but there are other ways to make it run with the 450's.

I have a 13.5:1 piston, a set of Hot Cams, and a few other odds and ends and I can easily out run a 450 in a drag race. As a matter of fact, I rode a 07 450 and was kind of disappointed in the power delivery compared to my dinosaur.

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  • GixRider

Posted May 07, 2007 - 09:37 PM


I went with a kit from Luke's racing. It's a 444 using a 12.5 compression wiesco piston. Overall I'm happy and have not had any issues with it. It hits much stronger down low but the top end kind of tapers off. If I had a set of aftermarket cams, I think this bike would be unstoppable.

I'd say to do cams or all the other small mods first unless you have money just burning a hole in your pocket. I did my own install so the cost was pretty low but I wouldn't want to pay somebody else for the moderate performance gain.

  • creeker

Posted May 08, 2007 - 04:45 AM


Heck, my 00' 426 is bone stock and will run right with a CRF450

  • Pincushion

Posted May 08, 2007 - 06:20 AM


the 97mm piston (444cc's) isn't going to blow you away. As stated above it'll give you a little more low end and tapers off earlier compared to stock. Since I ride trails its perfect, but if I we're looking for more top end juice I'd be looking at a 13.5:1 piston and some hotter cams.

The 444 kit is only worth it if you need you're cylinder repaired and a new piston.

  • Birdy426

Posted May 08, 2007 - 09:05 PM


I have the 444 kit from Luke's, a set of Hot Cams, and the 13.5:1 Wiseco piston...it rips. Love the power, no overheating issues, no reliability issues, but is a bit harder to start.

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